Warship Hazardous Prize (1706) a protected wreck site at risk

case study and quantitative analysis of dynamic seabed movement and rapid site

destruction by biological attack Data collated by the Warship Hazardous Prize (1706) Project Group (www.hazardousproject.info) for the Nautical Archaeology Society (www.nauticalarchaeologysociety.org) and Association of Protected Wreck Licensees (www.protectedwrecks.org.uk) as evidence to submit to the Marine Management Organisation, DEFRA and English Nature on the nature and extent of natural seabed movements and of destruction of underwater cultural heritage by marine wood boring organisms

Dr D. A. Johnston, Warship Hazardous Prize Project Group, Nautical Archaeology Society Trustee and Senior Tutor daj1u06@soton.ac.uk December 2014

Contents

(1) Introduction (2) Site Plans and Schematics (3) Multibeam sonar mapping of the seabed around the main site (4) Seabed movement monitoring studies - 1987 to 1988 (5) Seabed movement monitoring studies - 2002 to 2006 (6) Seabed movement monitoring 2008 to 2014 (7) Timber degradation survey

(1) Introduction

The remains of Warship Hazardous Prize 1706 lie wedged in a gulley in the reefs of the Bracklesham Beds in Bracklesham Bay, South of Chichester. The reef is overlaid with a layer of sand and the seabed in the area is highly dynamic and mobile, with continuous movement and changes in the level of the sand. The site is designated under the Protection of Wrecks Act 1973 and lies within a 100m diameter designated area. The site has been dived, studied, recorded, surveyed and investigated for over 30 years by the Sub Aqua Association Branch #308 and a wider group of helpers. Together these comprise the Warship Hazardous Prize Project Group (WHPPG). This provides an enormous amount of experience and factual data concerning seabed movement and dynamics which can only be obtained by regular underwater observation. In the years running up to 2008, ongoing measured monitoring of the seabed around the site and the remaining hull structure of Warship Hazardous Prize 1706 by WHPPG showed that

(1) significant changes in seabed level around the site were uncovering material which had never previously been seen, both within the hull structure, close to it and further afield within the designated area. This included 3 wooden barrels within the hull structure and a range of organic and inorganic artefacts from scattered locations (2) exposed underwater cultural heritage of an organic nature, including ship structure, provisions and cargo was at great risk of rapid external and internal attack by wood boring organisms (Limnoria (gribble) and Teredo (shipworm))

As a consequence, It was deemed both prudent and practical to seek an excavation licence under the Protection of Wrecks Act 1973 for a small, scale, research-led test excavation within the hull structure. The Licence was awarded for a test excavation in the 2008 season. All attempts to use that licence were thwarted by a combination of weather and changes to on site conditions resulting from dynamic seabed movement. In 2008, a team mobilised for an excavation week, but poor weather meant that only four days of the planned time were spent on site preparation and the rest of the week was postponed - no excavation was achieved In May 2009 a further mobilisation occurred, however, a large storm meant that operations were not possible and the week was postponed again In July 2009 a further mobilisation occurred, but once again stormy weather prevented work on site. In early 2010, diving by the WHPPG discovered that large sand overburden (over 1 metre in depth) had moved onto the site from the south over the winter. Such a large movement of sand had not been witnessed for over 20 years and it made excavation within the hull impractical as:

there would not have been enough time to remove the sand overburden

the area that would have needed to be cleared to ensure the sides of the trench were angled to prevent constant backfilling during excavation would have needed to be very large

However, conversely there had been a major movement of sand away from gullies in the underlying geology at the North - North West edge of the designated area. These had last been uncovered some 20 years previous and a range of artefacts recovered. The new exposure exposed further artefacts from the Hazardous wreck. After 2010, the sand overburden within the main site increased significantly in depth and extent such that in 2012-2013, only the very tops of the pile of cannon (port side of main site) the cannonball pile (starboard side of main site) and very few hull timbers (at the bow) remained visible. Work continued in the Northern gully area but this was also rapidly becoming recovered. Over the winter 2013-2014, a massive scouring occurred on the main site, likely as a result of the near continuous violent storms (and possibly also due to changes in currents within the bay resulting from the Environment Agency's managed coastal retreat programme at Medmerry and the ensuing coastal defence works at Bunn Leisure, both very close to the site). The 3 barrels within the hull, last seen in 2008, have been re-exposed and a 4th barrel has been observed close by, the top of the cannon pile (flush with the seabed in 2013) currently stands some 1.27 m proud of the surrounding seabed, representing a sediment loss of some 1.25m over a few months! and the cannonball pile (a regular monitoring point) is some 1.45 m proud and scoured out underneath such that there is almost a swim through, not previously seen.

As of 2014, the site is considered to currently be more exposed that in living memory and small and vulnerable artefacts are being exposed. In 2014 a further set of navigational dividers, an ornate shoe buckle and a small bronze pin have been exposed and recovered. Well preserved and archaeologically-significant timber artefacts including gun carriage axles and truck wheels have been observed, freshly exposed, on site and are under immediate threat of biological attack. These lie side by side and clearly represent ship stores being exposed for the first time in living memory (and from their condition, possibly for the first time since the original wrecking!). A small and ornate piece of turned wood has been observed attached to a concretion and several pieces of animal bone and parts of onion bottles observed. These may have since been lost as very poor visibility hampered work in 2014 and several storms have passed across the bay this autumn. Additionally, a minimum further 9 cannon have been exposed, lying some 100m from the main site, just within the designated area to the SW of the main site. These have never been seen before. The site is therefore currently even more exposed and at risk than it was in 2008 when the excavation licence was awarded. In the wider area, the reef to the south (the direction from which the sand had moved in) and east of the site is currently completely free of sand right out to the edge of the designated area. As a consequence of these natural and normal seabed changed, the site has been re entered onto English Heritage's "Heritage at Risk" register (https://www.english-heritage.org.uk/about/news/heritage-at-risk-2014/) In the context of seeking exemption from marine licensing for underwater archaeological investigations on designated wreck sites (including excavation), the following should also be born in mind.

The seabed is a highly dynamic environment subject to significant, unpredictable and rapid natural change and movement evidenced by "cycles" of sediment accumulation and scouring.

Only the top few cm of marine sediment are capable of supporting aerobic life; below these levels conditions are anoxic. This is why buried organic materials of archaeological significance are preserved so well underwater. Only a light covering with sediment is needed to place them beyond the reach of aerobic wood boring organisms organisms and deeper burial eliminates all but the hardiest of anaerobic saphrophytes.

Natural and routine seabed accumulations of only a few cm obliterate and destroy the organisms living in the top layers of sediment over massive areas on a regular basis. Similarly, seabed scouring of only a few cm disperses the motile organisms and expose the buried sessile organisms to predation - it is common in Bracklesham Bay to observe the seabed littered in toppled tubes of fan worms left vulnerable as the seabed has shifted and removed their supporting sediment.

The MMO licences activities across some 54,000 square kilometres. The total area included within the exclusion zones of all 46 protected wreck sites is under 5 square km (< 1/10,000

th of the total), the areas of archaeological deposit within the exclusion zones

is but a very small fraction of the overall designated area and the scale of any licensed intrusive activities involves but a tiny fraction of that. To put this into context, the combined intrusive effects on the marine environment of all of the activity ever licensed under the PoWA through its entire 40 year period on the Statute probably has caused less seabed disturbance than a single deployment of an inshore bottom trawl and a single bait digger in the intertidal zone probably disturbs and relocates more sediment in a single tidal window than most current archaeological excavations do in the entire project (a few cubic metres). The impact of archaeological activity in the dynamic and ever-changing underwater environment is so infinitesimally and unquantifiably small as to be insignificant and effectively zero.

Nature is both resilient and opportunistic. Site tags and datum poles erected on site and newly exposed cultural heritage are rapidly colonised with copious marine growth; when we had a diver trail operating across the site, we had to scrub the plastic navigation signs clean every month. Any temporary disturbance resulting from archaeological investigation will very rapidly be mitigated by nature itself.

(2) Site Plans and Schematics Since its discovery in 1977, the Warship Hazardous Prize 1706 site has been subject to continuous monitoring and survey. The following formal measured surveys and site schematics demonstrate large scale seabed movements and site destruction.

Site Plan - 1986 (north to left) - large section of timber and numerous guns (cannon) exposed at southern

end of main site, some hints of additional hull structure further north (to left), including additional guns

Site Plan - 1991 (north to left) - very significant scouring of sediment from north of main site exposed

substantial ship remains including the bow and parts of the forward port and starboard hull

Site Plan - 1996 (north to left) - entire southern end lost for ever (not buried, destroyed!). During 1994 and 1995 scouring occurred along the eastern side of the site progressing down to the southern end, in places this scouring was so severe that it exposed the natural clay bed. Scouring in southern and eastern parts of

the site caused new timbers to be exposed and exposed timbers to be moved off the site and lost. The whole of the southern end structure of the site started to break up in the winter of 1994 with continued loss

occurring through 1995. By the end of 1995 the complete loss of the southern frames together with most of the timbers in this area had occurred.

Site Schematic - 2006 (north to left) - scouring out of the internal area of the site in 2005-2006 revealed significant archaeological material which had not previously been seen, including three barrels at the SW

end.

Site Schematic - 2010 (north to left) - 2009-2010 saw a large area of sand overburden (yellow) sweep over the site from the south, burying the southern-most loose guns, filling the hull structure by up to an additional

metre (reburying the material exposed in 2006, and parts of the surviving hull structure) and covering the reef around the site

Site Schematic - 2012 (north to left) - by 2012, the majority of the site except for the very highest points were completely covered in sand - the sand bar extended at least 50 m all around the site and continued to rise to

the south and east

Site Schematic - 2014 (north to left) - the winter storms of 2013-2014 completely scoured away the sand

from around the site, exposing the underlying reef across a very significant area, especially to the S and W (see multibeam sonar data in section 3 below). Within the hull, the sand overburden was stripped back beyond the level seen in 2006, re-revealing the barrels, exposing other ships timbers and stores further

towards the beak (never previously seen) and exposing significant areas of well preserved hull frame and planking along the starboard side spanning between the beak and the cannonball pile.

Photomosaic - timbers exposed all; along the starboard side in 2014

(3) Multibeam sonar mapping of the seabed around the main site A variety of professional multibeam sonar surveys of the main site have been undertaken over the years and provide "snapshots" of the state of the seabed, areas of sand and areas of exposed reef in the wider area. These surveys document significant changes in areas of exposed reef but were all commissioned at times that the archaeological site was exposed, reflecting more limited areas of sand.

2002 Reson multibeam survey (north up) - extensive reef exposed to immediate W, S and E of main site,

large sand bar immediately N of main site and to S and E of main site,

2003 Wessex multibeam survey (north up) - extensive reef exposed to immediate W, S and E of main site,

large sand bar immediately N of main site and to S and E of main site,

2014 Wessex multibeam survey (north up) - massive scouring of reef line to S of main site, and reef to W

and N of main site

(4) Seabed movement monitoring studies - 1987 to 1988 During 1987 and 1988 sediment levels were measured against fixed datum sites for the northern, central and southern parts of the site (datum points D6 (southern), D7 (central) and D4 (northern)).

1987 - 1988 seabed movements (distance from top of datum down to seabed) Sediment level changes

during this period show an approximate 400mm loss occurring along the northern and central parts of the site and an approximately 100mm loss and regain in the southern end of the site.

(5) Seabed movement monitoring 2002 to 2006 In the summer of 2002 a new series of sediment monitoring points were established around the forward end of the site. These were put in place to gather direct, measured evidence of sediment movements and to measure the degree of change occurring in the specific areas where they were situated.

2002 - 2006 seabed movements (distance from top of datum down to seabed). The data clearly shows large

sediment movements measured during the period from 2002 to 2005. The general trend appears to be accretion occurring mid way through each year with a slow decline in sediment levels towards the end of the diving season. This pattern of accretion and scouring appears to be roughly cyclical, although the degree of change occurring varies yearly with sediment movements ranging from 100mm for certain years (2004) to in

excess of 200mm for other years (2003 and 2005) (note that measurements are not obtained during the winter months when environmental conditions precluded diving). However, when comparing sediment levels at the end of one diving season and the beginning of the next it is possible to see clear changes occurring.

These reflect scouring and accretion events that are not recorded in such frequency as those occurring over the summer season.

2002 - 2006 seabed movements (distance from top of datum down to seabed) related to location on site. It is

apparent that along the western side of the site (M1 to M5) and the northern edge of the site (M10) there were small degrees of sediment movement occurring, although localised scouring does occur. Along the

eastern side of the site (M9 to M6) the sediment processes were more dynamic with large changes of accretion and scouring. These dynamic changes also affect the amidships section of the site (M6) and to a

lesser extent (M5).

2004 seabed movements (distance from top of datum down to seabed) at M10 datum - 50mm accumulation

in 3 months

2005 seabed movements (distance from top of datum down to seabed) at M1, M2, M3, M4

125mm loss in 5 months followed by 175mm accumulation in 1 month at M1

Summary of seabed movements 2002-2006

(6) Seabed movement monitoring studies 2011 to 2014 Measurement of established points on the wreck structure to seabed on outside of hull

Date Top of 3 cannon. Top of Cannonball mound. M9 Breast Hook. M10 Beak.

31st July 2011 840mm 730mm 600mm 710mm

21st April 2013 1250mm 1500mm 720mm 500mm

29th June 2013 1200mm 990mm 740mm 560mm

25th August 2013 1100mm 1010mm 750mm 560mm

21April 2014 1250mm 1440mm 820mm 540mm

4th May 2014 1032mm 1450mm 810mm 560mm

26th May 2014 1420mm not taken not taken not taken

22nd

June 2014 1270mm 1450mm 840mm 540mm

27th July 2014 1390mm 1450mm 830mm 540mm

14th Sept. 2014 1400mm 1550mm 820mm 560mm

Notes:

no measurements taken in 2012 as most of site effectively buried

Additional measurement taken on 21st April 2014:top of gun J (nearly buried in 2012-13)

= 1009mm

(7) Timber degradation survey Timber degradation monitoring points were put in place on ship timbers during 2002, at the same time as the sediment monitoring points were established. These were all situated in the amidships area close to sediment monitoring point M5.

During the 2004 and 2005 season losses of timber length of up to 173mm were recorded for H3.

By the end of 2005, a loss of 260mm at H5 was recorded. These changes prove the rapid degradation suffered by exposed timbers (often oak frames, considered a highly durable timber) through attack by marine wood boring organisms. Sediment scouring is directly related to the increased exposure and subsequent degradation of timbers through Limnoria (gribble) attack, especially where end grain is exposed. Limnoria is endemic in the local environment and the surface of freshly exposed wood can be completely destroyed within weeks of exposure. Live shipworm (Teredo sp.) have also been observed on several timbers in the site over the past few years, where gribble attack has exposed the Teredo burrows within the timber - Teredo can completely eat away timber from the inside. Such destruction means that opportunities to study tool marks and shipwright marks and to acquire dendrochronological data are rapidly lost and emphasise the need to be able to reactively and rapidly protect freshly exposed timbers by covering with geotextile and or sandbags - these activities currently represent deposits and dredging / removals and require marine licensing. The current licensing process simply cannot react fast enough to prevent significant damage to newly exposed cultural heritage and so an exemption for the protective covering of cultural heritage is urgently required.

Summary of identified risks to Warship Hazardous Prize 1706 site